Multi-step flow cleaning method and multi-step flow cleaning apparatus

ABSTRACT

A multi-step flow cleaning method and a multi-step flow cleaning apparatus are provided which effectively clean workpieces with a stream of a cleaning solution and to suppress an increase of foreign matters adhering to the surfaces of the workpieces. A cleaning tank  10  for holding workpieces is provided, a supply line  14  for supplying a cleaning solution such as pure water from the bottom surface of the cleaning tank is provided, and a valve  12  for adjusting the flow of the cleaning solution is disposed in the middle of the supply line  14 . The valve  12  is equipped with a switching section  12   a  for controlling the outflow of the cleaning solution by opening or closing the supply line  14 , and a bypass  12   b  for supplying the cleaning solution, bypassing the switching section  12   a . The valve  12  is provided such that it is able to adjust in two steps the supply flow of the cleaning solution supplied to the cleaning tank  10  by using the supply flow fed through the bypass  12   b  and the supply flow fed through the switching section  12   a.

FIELD OF THE INVENTION

The present invention relates to a multi-step flow cleaning method and amulti-step flow cleaning apparatus and, more particularly, to amulti-step flow cleaning method and a multi-step flow cleaning apparatusadapted to clean an workpiece by placing the workpiece, which has beentreated with a chemical, in a cleaning tank and by supplying a cleaningsolution thereby to clean the workpiece with the stream of the cleaningsolution.

BACKGROUND ART

Hitherto, workpieces to be cleaned including semiconductor wafers, glasssubstrates, and electronic substrates are required to be subjected to acleaning process for cleaning with a cleaning solution such as purewater to remove a chemical from the surfaces of the workpieces that havebeen subjected to a chemical treatment (etching). In this cleaningprocess, a cleaning apparatus is extensively used in which workpiecesthat have been subjected to the chemical treatment are placed, and acleaning solution such as pure water is supplied from the bottom surfaceof the cleaning tank thereby to clean the workpieces by the stream ofthe cleaning solution.

FIG. 11 is a piping diagram showing the structure of a conventionalcleaning apparatus adapted to clean workpieces with the stream of acleaning solution by supplying the cleaning solution into the cleaningtank as described above.

As shown in FIG. 11, the conventional cleaning apparatus is providedwith a cleaning tank 20 for holding workpieces (not shown) that havebeen treated with a chemical, a supply line 24 for supplying a cleaningsolution such as pure water from the bottom surface of the cleaning tank20, and a valve 22 connected at the middle of the supply line 24 tocontrol the supply of the cleaning solution.

The valve 22 has a structure for opening or closing the supply line byelectrically turning it ON or OFF. This enables the valve 22 to supplyor interrupt the supply of the cleaning solution, which flows outthrough the supply line 24, to the cleaning tank 20.

When using the conventional cleaning apparatus, first, a plurality ofworkpieces, which have been subjected to a chemical treatment such asetching in a predetermined process, are placed in a cleaning cassette(not shown), and the cleaning cassette (not shown) is carried into thecleaning tank 20. When the cleaning cassette (not shown) has beencarried into the cleaning tank 20, a cleaning solution such as purewater, which has been supplied through the supply line 24, is let flowinto the cleaning tank 20 by opening the valve 22.

FIG. 12 is a graph showing changes in the flow of the cleaning solutionsupplied while the conventional cleaning apparatus shown in FIG. 11 isin the cleaning operation. As shown in FIG. 11, a constant flow of thecleaning solution is supplied into the cleaning tank 20 at all timesuntil the cleaning is finished after the valve 22 is opened. Thecleaning solution supplied in the constant flow flows into the cleaningcassette (not shown) placed in the cleaning tank 20 to clean thesurfaces of the workpieces by the stream of the cleaning solution.

Thus, the conventional cleaning apparatus has been cleaning the surfacesof the workpieces held in the cleaning cassette (not shown) with theconstant flow by supplying the constant stream of the cleaning solutionthrough the supply line 24 connected to the bottom surface of thecleaning tank 20.

The conventional cleaning apparatus is capable of removing some foreignmatters, which have adhered to the surfaces of the workpieces during thechemical treatment, by the stream of the cleaning solution supplied tothe cleaning tank; however, the stream of the cleaning solution suppliedin the constant flow is not good enough to remove some persistentforeign matters on the workpieces. Hence, it has been difficult for theconventional cleaning apparatus to remove the foreign matters, whichhave adhered during the chemical treatment process, to a satisfactorylevel.

Further, the conventional cleaning apparatus requires a large quantityof a cleaning solution and a long cleaning time in order to fully removepersistent foreign matters, which have adhered to the surfaces ofworkpieces during a chemical treatment process. Hence, it has beendifficult to reduce a cleaning solution or shorten the cleaning time inimplementing satisfactory cleaning of workpieces.

It is an object of the present invention to solve the problems describedabove and to provide a multi-step flow cleaning method and a multi-stepflow cleaning apparatus that are capable of cleaning workpieces moreeffectively with the stream of a cleaning solution and also capable ofsuppressing an increase in foreign matters adhering to the surfaces ofthe workpieces.

DISCLOSURE OF THE INVENTION

To this end, according to one aspect of the present invention, there isprovided a cleaning method by placing workpieces in a cleaning tank andby supplying a cleaning solution so as to clean the workpieces with aflow of the cleaning solution, wherein the flow of the cleaning solutionsupplied to the cleaning tank is adjusted to change the stream during acleaning operation, thus cleaning the workpieces with the changingstream of the cleaning solution. In this case, the flow of the cleaningsolution supplied to the cleaning tank is either changed from a smallflow to a large flow in steps or continuously changed from a small flowto a large flow. Further, the supply flow of the cleaning solution isheld small at least until the workpieces are fully immersed in thecleaning solution supplied to the cleaning tank.

According to another aspect of the present invention, there is provideda cleaning apparatus for cleaning workpieces by placing the workpiecesin a cleaning tank and by providing the cleaning tank with a supply lineto supply a cleaning solution so as to clean the workpieces with thestream of the cleaning solution, the cleaning apparatus being providedwith a supply line for supplying the cleaning solution to the cleaningtank, and a flow adjusting means which is provided on the supply lineand which adjusts the flow of the cleaning solution supplied to thecleaning tank, wherein the flow of the cleaning solution supplied to thecleaning tank is adjusted by the flow adjusting means to change thestream so as to clean the workpieces by the changing stream of thecleaning solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping diagram showing the structure of a first embodimentof a multi-step flow cleaning apparatus in accordance with the presentinvention.

FIG. 2 is a graph illustrating the changes in the flow of a cleaningsolution supplied while the multi-step flow cleaning apparatus shown inFIG. 1 is in a cleaning operation.

FIG. 3 is a piping diagram showing the structure of a second embodimentof a multi-step flow cleaning apparatus in accordance with the presentinvention.

FIG. 4 is a graph illustrating the changes in the flow of a cleaningsolution supplied while the multi-step flow cleaning apparatus shown inFIG. 3 is in a cleaning operation.

FIG. 5 is a piping diagram showing the structure of a third embodimentof a multi-step flow cleaning apparatus in accordance with the presentinvention.

FIG. 6 is a graph illustrating the changes in the flow of a cleaningsolution supplied while the multi-step flow cleaning apparatus shown inFIG. 5 is in a cleaning operation.

FIG. 7 is a piping diagram showing the structure of a fourth embodimentof a multi-step flow cleaning apparatus in accordance with the presentinvention.

FIG. 8 is a graph illustrating the changes in the flow of a cleaningsolution supplied while the multi-step flow cleaning apparatus shown inFIG. 7 is in a cleaning operation.

FIG. 9 is a graph showing an increase in the number of foreign mattersobserved when a cleaning experiment has been carried out with aconventional cleaning apparatus shown in FIG. 11.

FIG. 10 is a graph showing an increase in the number of foreign mattersobserved when a cleaning experiment has been carried out with themulti-step flow cleaning apparatus in accordance with the presentinvention shown in FIG. 1.

FIG. 11 is a piping diagram showing the structure of the conventionalcleaning apparatus.

FIG. 12 is a graph illustrating the changes in the flow of a cleaningsolution supplied while the conventional cleaning apparatus shown inFIG. 11 is in a cleaning operation.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will describe in detail the embodiments of a multi-stepflow cleaning method and a multi-step flow cleaning apparatus inaccordance with the present invention with reference to the accompanyingdrawings.

FIG. 1 is a piping diagram showing the structure of a first embodimentof a multi-step flow cleaning apparatus in accordance with the presentinvention. Further, FIG. 2 is a graph illustrating the changes in theflow of a cleaning solution supplied while the multi-step flow cleaningapparatus shown in FIG. 1 is in a cleaning operation.

As shown in FIG. 1, the first embodiment of the multi-step flow cleaningapparatus in accordance with the present invention is provided with acleaning tank 10 for holding workpieces (not shown) that have undergonea chemical treatment, a supply line 14 connected to the bottom surfaceof the cleaning tank 10 to supply a cleaning solution such as pure waterfrom outside, and an adjusting valve 12 disposed in the middle of thesupply line 14 to adjust the flow of the cleaning solution such as purewater.

The adjusting valve 12 is provided with a switching section 12 a foropening/closing the supply line 14 by being electrically turned ON/OFF,and a bypass 12 b provided so that it bypasses the switching section 12a. Hence, unlike in the case of a conventional cleaning apparatus, theadjusting valve 12 is able to adjust the flow of a cleaning solution intwo steps as time passes according to the supply flow through theswitching section 12 a and the supply flow through the bypass 12 b.

When using the multi-step flow cleaning apparatus configured asdescribed above, first, a plurality of workpieces are taken from apredetermined process and placed in a cleaning cassette (not shown), andthe cleaning cassette (not shown) is carried into the cleaning tank 10.When the cleaning cassette (not shown) has been carried into thecleaning tank 10, a cleaning solution such as pure water is flown intothe cleaning tank 10 through the supply line 14.

At this time, the switching section 12 a of the adjusting valve 12 isheld closed thereby to cause the cleaning solution, which has beensupplied to the supply line 14, to flow into the cleaning tank 10through the bypass 12 b. The cleaning solution flown into the cleaningtank 10 moves from the bottom to top of the cleaning cassette (notshown) to clean the surfaces of the contained workpieces with the streamthereof.

After the workpieces have been cleaned for a given time by the cleaningsolution supplied through the bypass 12 b, the adjusting valve 12 opensthe switching section 12 a to supply the cleaning solution also throughthe switching section 12 a in addition to the bypass 12 b.

Thus, in the first embodiment, as shown in FIG. 2, the workpieces arecleaned with the stream of the cleaning solution supplied in a smallflow through the bypass 12 b, with the valve 12 closed in a first step.Then, after the cleaning operation of the workpieces in the first stephas been carried out for a given time, the switching section 12 a of theadjusting valve 12 is opened in a second step to supply the cleaningsolution through the bypass 12 b and the switching section 12 a at thesame time so as to clean the workpieces with a larger flow. Thus, thecleaning solution supplied into the cleaning tank 10 performs thecleaning operation of the workpieces, which have been placed in thecleaning tank 10, with the stream of the cleaning solution that ischanged in two steps.

According to the first embodiment, therefore, the workpieces are cleanedwith pure water flow in two steps based on lapse of time; hence, theforeign matters on the surfaces of the workpieces can be effectivelyremoved, allowing a shortened cleaning time and a reduced quantity ofcleaning solution to be achieved.

Referring now to FIG. 3 and FIG. 4, a second embodiment of themulti-step flow cleaning method and the multi-step flow cleaningapparatus in accordance with the present invention will be described indetail. FIG. 3 is a piping diagram showing the structure of the secondembodiment of the multi-step flow cleaning apparatus in accordance withthe present invention. FIG. 4 is a graph illustrating the changes in theflow of a cleaning solution supplied while the multi-step flow cleaningapparatus shown in FIG. 3 is in a cleaning operation. In the secondembodiment, a plurality of the adjusting valves 12 in the firstembodiment have been installed, and the same components will be assignedthe same reference numerals, and the explanation thereof will not berepeated.

As shown in FIG. 3, the second embodiment of the multi-step flowcleaning apparatus in accordance with the present invention is providedwith a cleaning tank 10 for holding workpieces, a supply line 14 forsupplying a cleaning solution such as pure water, and a plurality ofadjusting valves 12-1 and 12-2 disposed in series in the supply line 14,and a valve 16.

The valve 16 is provided so that it is electrically turned ON and OFF toopen and close the supply line. The adjusting valves 12-1 and 12-2 areprovided with a switching section 12 a for opening and closing thesupply line 14 by electrically turning it ON and OFF and a bypass 12 bprovided so that it bypasses the switching section 12 a. Hence, thesecond embodiment is able to change the flow of a cleaning solution in aplurality of steps as time passes by the adjusting valves 12-1 and 12-2,and the valve 16.

When using the multi-step flow cleaning apparatus configured asdescribed above, first, a plurality of workpieces are taken from apredetermined process and placed in a cleaning cassette (not shown), andthe cleaning cassette (not shown) is carried into the cleaning tank 10.When the cleaning cassette (not shown) has been carried into thecleaning tank 10, a cleaning solution such as pure water is flown intothe cleaning tank 10 through the supply line 14.

At this time, the adjusting valves 12-1 and 12-2 hold the switchingsections 12 a-1 and 12 a-2 in a closed state. Under this condition, thevalve 16 is opened to supply the cleaning solution into the cleaningtank 10 through the bypasses 12 b-1 and 12 b-2 of the adjusting valves12-1 and 122 to clean the workpieces.

After the workpieces have been cleaned for a given time under such acondition, the switching section 12 a-2 of the adjusting valve 12-2 ischanged over from the closed state to an open state. This causes a largeflow of the cleaning solution to flow into the cleaning tank 10 throughthe bypass 12 b-2 and the switching section 12 a-2 via the bypass 12 b-1of the adjusting valve 12-1, thereby cleaning the surfaces of theworkpieces.

Further, after cleaning with the large flow for a given time, theswitching section 12 a-1 of the adjusting valve 12-1 is changed overfrom the closed state to the open state. This causes a further largeflow of cleaning solution to be supplied into the cleaning tank 10through the adjusting valves 12-1 and 12-2 to clean the surfaces of theworkpieces.

Thus, in the second embodiment, the workpieces are cleaned with thecleaning solution that is supplied by opening the valve 16 in a firststep as shown in FIG. 4. After the cleaning operation of the workpieceshas been implemented for the given time in the first step, the switchingsection 12 a-2 of the adjusting valves 12-2 is opened in a second stepto clean the workpieces. Further, after the cleaning operation of theworkpieces has been implemented for a given time in the second step, theswitching section 12 a-1 of the adjusting valves 12-1 is opened in athird step to clean the workpieces. In this manner, the workpiecesplaced in the cleaning tank 10 can be cleaned with the stream of thecleaning solution which is supplied to the cleaning tank 10 such that itis changed in three steps.

According to the second embodiment, therefore, the workpieces arecleaned with pure water flow in three steps based on lapse of time;hence, the foreign matters on the surfaces of the workpieces can beeffectively removed, allowing a shortened cleaning time and a reducedquantity of cleaning solution to be achieved. The second embodimentmakes it possible to implement more effective cleaning than thatachieved by the first embodiment.

Referring now to FIG. 5 and FIG. 6, a third embodiment of the multi-stepflow cleaning method and the multi-step flow cleaning apparatus inaccordance with the present invention will be described in detail. FIG.5 is a piping diagram showing the structure of the third embodiment ofthe multi-step flow cleaning apparatus in accordance with the presentinvention. FIG. 6 is a graph illustrating the changes in the flow of acleaning solution supplied while the multi-step flow cleaning apparatusshown in FIG. 5 is in a cleaning operation. The third embodiment has thesame components except for the adjusting valve 12 in the firstembodiment, and the same components will be assigned the same referencenumerals, and the explanation thereof will not be repeated.

As shown in FIG. 5, the third embodiment of the multi-step flow cleaningapparatus in accordance with the present invention is provided with acleaning tank 10 for holding workpieces, supply lines 14-1 and 14-2branched into two in parallel from the bottom of the cleaning tank 10 torespectively supply a cleaning solution such as pure water, and valves16-1 and 16-2 disposed in the supply lines 14-1 and 14-2, respectively,which are arranged in parallel. The valves 16-1 and 16-2 are provided sothat they are electrically turned ON and OFF to open and close thesupply lines. The valve 16-2 is provided such that it is able to supplya large flow of the cleaning solution than the valve 16-1 is. Hence, thethird embodiment is able to change the flow of the cleaning solution inthree steps as time passes by means of the flow supplied through thevalve 16-1, the flow supplied through the valve 16-2, and the flowsupplied through both valves 16-1 and 16-2 at the same time.

When using the multi-step flow cleaning apparatus in accordance with thepresent invention configured as described above, first, a plurality ofworkpieces are taken from a predetermined process and placed in acleaning cassette (not shown), and the cleaning cassette (not shown) iscarried into the cleaning tank 10. When the cleaning cassette (notshown) containing the workpieces therein has been carried into thecleaning tank 10, a cleaning solution such as pure water is flown intothe cleaning tank 10.

At this time, the valve 16-2 is held in a closed state. The valve 16-1is gradually opened from the closed state. This causes the cleaningsolution to be supplied into the cleaning tank 10 through the valve 16-1to clean the workpieces.

After the workpieces have been cleaned for a given time under such acondition, the valve 16-1 is closed, whereas the valve 16-2 is openedfrom the closed state. This causes the cleaning solution to be suppliedinto the cleaning tank 10 through the valve 16-2 to clean theworkpieces.

Further, after performing the cleaning operation for the given timeunder such a condition, the valves 16-1 and 16-2 are opened at the sametime. This causes a larger flow of the cleaning solution to be suppliedinto the cleaning tank 10 through the valves 16-1 and 16-2 to clean theworkpieces.

Thus, in the third embodiment, the workpieces are cleaned by opening thevalve 16-1 in a first step as shown in FIG. 6. After the cleaningoperation of the workpieces has been implemented for the given time inthe first step, the valve 16-1 is closed, whereas the valve 16-2 isopened in a second step to clean the workpieces. Further, after thecleaning operation of the workpieces has been implemented for a giventime in the second step, the valves 16-1 and 16-2 are opened at the sametime in a third step to clean the workpieces. In this manner, theworkpieces placed in the cleaning tank 10 can be cleaned with the streamof the cleaning solution which is supplied to the cleaning tank 10 suchthat it is changed in three steps.

According to the third embodiment having the foregoing configuration,the workpieces are cleaned by changing the flow of the cleaning solutionin three steps with the lapse of time; hence, the foreign matters on thesurfaces of the workpieces can be effectively removed, allowing ashortened cleaning time and a reduced quantity of cleaning solution tobe achieved. The third embodiment makes it possible to obtain the sameadvantage as that obtained by the second embodiment.

Referring now to FIG. 7 and FIG. 8, a fourth embodiment of themulti-step flow cleaning method and the multi-step flow cleaningapparatus in accordance with the present invention will be described indetail. FIG. 7 is a piping diagram showing the structure of the fourthembodiment of the multi-step flow cleaning apparatus in accordance withthe present invention. FIG. 8 is a graph illustrating the changes in theflow of a cleaning solution supplied while the multi-step flow cleaningapparatus shown in FIG. 7 is in a cleaning operation. The fourthembodiment has the same components except for the adjusting valve 12 inthe first embodiment, and the same components will be assigned the samereference numerals, and the explanation thereof will not be repeated.

As shown in FIG. 7, the fourth embodiment of the multi-step flowcleaning apparatus in accordance with the present invention is providedwith a cleaning tank 10 for holding workpieces, a supply line 14 forsupplying a cleaning solution such as pure water from the bottom of thecleaning tank 10, a valve 16 disposed in the supply line 14, and aregulator 18 for adjusting the flow of the cleaning solution suppliedthrough the valve 16.

The valve 16 is provided so that it is electrically turned ON and OFF toopen and close the supply line. The regulator 18 is provided so that itadjusts the flow of the cleaning solution supplied through the valve 16by a voltage or pneumatic drive pressure. Therefore, in the fourthembodiment, the flow supplied through the valve 16 can be continuouslychanged by the regulator 18 as time passes.

When using the multi-step flow cleaning apparatus in accordance with thepresent invention configured as described above, first, a plurality ofworkpieces are taken from a predetermined process and placed in acleaning cassette (not shown), and the cleaning cassette (not shown) iscarried into the cleaning tank 10. When the cleaning cassette (notshown) has been carried into the cleaning tank 10, a cleaning solutionsuch as pure water is flown into the cleaning tank 10.

At this time, the valve 16 is held in an opened state, and the regulator18 is driven to continuously change the flow of the cleaning solutionsupplied into the cleaning tank 10. This causes the cleaning solution tobe supplied into the cleaning tank 10 through the regulator 18 to cleanthe workpieces.

Thus, in the fourth embodiment, the regulator 18 continuously increasesthe flow of the cleaning solution when the valve 16 is opened as shownin FIG. 8. The regulator 18 supplies the cleaning solution in a fixedflow after a predetermined time passes. Hence, the workpieces arecleaned with the cleaning solution supplied by the regulator 18 into thecleaning tank 10 in such a manner that they are first cleaned with thestream of the cleaning solution that continuously increases, thencleaned with the fixed flow of the cleaning solution after thepredetermined time passes. According to the fourth embodiment having theforegoing configuration, the workpieces are cleaned with the pure waterflow that continuously increases as time passes; hence, contaminants onthe surfaces of the workpieces can be effectively removed, allowing ashortened cleaning time and a reduced quantity of cleaning solution tobe achieved

The embodiments of the multi-step flow cleaning method and themulti-step flow cleaning apparatus in accordance with the presentinvention have been described above. The present invention will now bedescribed in more detail by means of working examples.

Working Examples

FIG. 9 is a graph illustrating an increase in the number of foreignmatters observed when a cleaning experiment was carried out with theconventional cleaning apparatus shown in FIG. 11. FIG. 10 is a graphillustrating an increase in the number of foreign matters observed whena cleaning experiment was carried out with the multi-step flow cleaningapparatus shown in FIG. 1.

As shown in FIG. 9, in the cleaning experiment with the conventionalcleaning apparatus, workpieces were cleaned with pure water flows of 10L/min and 30 L/min, respectively, for 10 min., 15 min., and 20 min.,respectively.

As illustrated in FIG. 10, in order to compare the multi-step flowcleaning apparatus in accordance with the present invention with theconventional cleaning apparatus, the three different cleaningexperiments were carried out with the cleaning apparatus in accordancewith the present invention as follows: workpieces were cleaned with asmall flow of 10 L/min for 1 min. and a large flow of 30 L/min for 10min. totaling 11 min.; workpieces were cleaned with a small flow of 10L/min for 3 min. and with a large flow of 30 L/min for 10 min., totaling13 min.; and workpieces were cleaned with a small flow of 10 L/min for10 min. and a large flow of 30 L/min for 10 min., totaling 20 min.

As the workpieces to be cleaned, substrates which are composed of baresilicon substrates sandwiched between silicon substrates coated withoxide silicon films and which are treated with fluorine acid were used.The number of increased foreign matters was calculated as follows: thenumber of foreign matters adhered to the surfaces of the workpieces wasmeasured before the chemical treatment and after the cleaning process,respectively, and the number of the foreign matters before the chemicaltreatment was subtracted from the number of the foreign matters afterthe cleaning process. In the graphs provided in FIG. 9 and FIG. 10, theforeign matters measuring 0.13 to 0.3 μm are indicated by hatched bars,and the foreign matters measuring 0.3 μm or more are indicated by blankbars, respectively.

As shown in FIG. 9, it is seen that the conventional cleaning apparatushas a tendency in which the increase of the foreign matters reduces asthe treatment time is prolonged in both cases wherein the pure waterflows were 10 L/min and 30 L/min, whereas approximately 200 to 1000 pcs.of foreign matters are always left unremoved even after the cleaning wascontinued for 20 minutes.

On the other hand, in the case of the multi-step flow cleaning apparatusin accordance with the present invention shown in FIG. 10, it is seenthat the increase in the number of the foreign matters was controlled toapproximately 200 pcs. or less in comparison with the case of theconventional cleaning apparatus, when the cleaning operation was carriedout at the small flow for 3 min. and at the large flow for 10 min.,totaling 13 minutes.

Therefore, the use of the multi-step flow cleaning method and themulti-step flow cleaning apparatus in accordance with the presentinvention makes it possible to reduce an increase in the number offoreign matters, shorten the required cleaning time, and to effectivelyreduce the quantity of a cleaning solution consumed for cleaning.

The multi-step flow cleaning method and the multi-step flow cleaningapparatus made by the present invention have been described in detail.The present invention, however, is not limited to the embodimentsdiscussed above; modifications can be made without departing from thespirit and scope of the present invention.

For instance, the number of the adjusting valves 12 described in theembodiments is not limited to the numbers mentioned in the embodiments;it may be increased as necessary.

Industrial Applicability

Thus, the multi-step flow cleaning method and the multi-step flowcleaning apparatus make it possible to reduce an increase in the numberof foreign matters and to accomplish efficient cleaning process bychanging intermittently or continuously the flow of pure water suppliedduring a cleaning process.

What is claimed is:
 1. A multi-step flow cleaning method comprising: placing a workpiece in a cleaning tank; supplying a cleaning solution to the cleaning tank to clean the workpiece with a stream of the cleaning solution; and adjusting a flow of the cleaning solution to the cleaning tank during a cleaning operation in such a manner that a flow rate is stepwisely increased.
 2. The multi-step flow cleaning method according to claim 1, wherein: the flow rate supplied to the cleaning tank is increased after the workpiece is fully immersed into the cleaning solution.
 3. A multi-step flow cleaning method comprising: placing a workpiece in a cleaning tank; supplying a cleaning solution to the cleaning tank to clean the workpiece with a stream of the cleaning solution; and adjusting a flow of the cleaning solution supplied to the cleaning tank during a cleaning operation in such a manner that a flow rate is linearly increased and then held constant.
 4. The multi-step flow cleaning method according to claim 3, wherein: the flow rate supplied to the cleaning tank is increased after the workpiece is fully immersed into the cleaning solution. 